A Novel Combinatorial Epigenetic Therapy Using Resveratrol and Pterostilbene for Restoring Estrogen Receptor-α (ERα) Expression in ERα-Negative Breast Cancer Cells

Breast cancer is the second most common cancer and a leading cause of cancer death in women. Specifically, estrogen receptor-alpha (ER alpha)-negative breast cancers are clinically more aggressive and normally do not respond to conventional hormone-directed therapies such as tamoxifen. Although epigenetic-based therapies such as 5-aza-2'-deoxycytidine and/or trichostatin A as DNA methyltransferase (DNMT) and histone deacetylase (HDAC) inhibitors, respectively, can regulate the expression of ER alpha, this can often lead to a number of side effects. Plant-based dietary compounds such as resveratrol and pterostilbene in novel combinatorial therapy provides new avenues to target these side effects and provide similar results with a higher level of safety. Here, we report that combinatorial resveratrol and pterostilbene leads to the reactivation of ER alpha expression in ER alpha-negative breast cancer cells in a time-dependent manner. Chromatin immunoprecipitation analysis of the ER alpha promoter in each cell type revealed an increase in enrichment of acetyl-H3, acetyl-H3lysine9 (H3K9) and acetyl-H4 active chromatin markers in the ER alpha promoter region after combinatorial treatment. This treatment also resulted in a significant change in HDAC and histone acetyl transferase (HAT) enzyme activity in these cells after 3 days of treatments. The combination resulted in a significant decrease in DNMT enzyme activity and 5-methylcytosine levels in MDA-MB-157 breast cancer cells. Moreover, reactivation of ER alpha expression by resveratrol combined with pterostilbene was found to sensitize ERa-dependent response to 17 beta-estradiol (E2)-mediated cellular proliferation and antagonist 4-hydroxytamoxifen (4-OHT)-mediated inhibition of cellular proliferation in ER alpha-negative breast cancer cells. E2 and 4-OHT further affected the ER alpha-responsive downstream progesterone receptor (PGR) gene in ER alpha reactivated MDA-MB-157 cells. Collectively, our findings provide a new and safer way of restoring ERa expression by regulating epigenetic mechanisms with the use of phyto-chemicals in combinatorial therapy. This combination can further provide effective treatment options for hormonal refractory breast cancer with available anti-hormonal therapy.